In a mixing bowl, combine chopped boneless, skinless chicken breasts with soy sauce, cornstarch, rice wine vinegar, sesame oil, ground ginger, and white pepper. Set aside to marinate for at least 30 minutes.

Bring a large pot of salted water to a rolling boil. Add lo mein noodles and cook according to package instructions until al dente, about 6–8 minutes. Drain and rinse under cold water.

In a separate bowl, whisk together soy sauce, oyster sauce, brown sugar, cornstarch, sesame oil, rice wine vinegar, chicken broth, and white pepper until smooth.

Heat a wok or large skillet over medium-high heat with a splash of oil. Add marinated chicken and stir-fry for about 5–6 minutes until cooked through and lightly browned. Remove and set aside.

In the same wok, add sliced bell peppers, mushrooms, and shredded carrots. Stir-fry for about 3–4 minutes until tender-crisp.

Return cooked chicken to the wok and pour prepared sauce over the entire mixture. Stir gently to combine and cook for another 2–3 minutes until the sauce begins to thicken.

Add prepared noodles and toss until well-coated in the sauce. Transfer to serving plates or bowls and garnish with sliced green onions.